Time of Sampling

Season to season fluctuations in vegetation attributes represent the key consideration when deciding what time of year to conduct rangeland inventory or monitoring programs. To prevent seasonal differences from confounding interpretations, comparisons between inventory data from various sites or monitoring data from a single site over a number of years, should be confined to the same season so that key species are at a similar level of maturity. Also, it is possible to select vegetation attributes that are relatively insensitive to seasonal fluctuations, such as basal cover, to minimize the effects of sampling during different seasons.

The best time of the year to sample depends upon the objectives of the program and the selection of attributes to be measured. For example, regular monitoring to evaluate stocking rates by determining utilization levels are best conducted at the end of the grazing season. If species composition is identified as a monitored attribute, more accurate data collection is possible by coinciding field work with the period when plants are flowering and identifiable.

Other secondary factors may also control the most practical time of sampling. For example, sampling opportunities may be restricted by boggy soils limiting the accessibility to high elevation sites during spring, the availability of skilled labor, or conflicting workplace commitments.

References and Further Reading

Bureau of Land Management. 1996. Sampling vegetation attributes. Interagency Technical Reference, BLM/RS/ST-96/002+1730. pp 1-29.

McClaran, M.P., and D.N. Cole. 1993. Packstock in wilderness: Use, impacts, monitoring, and management. General Technical Report INT-301. Intermountain Research Station, United States Department of Agriculture, Forest Service. Ogden, UT. p 13.

Smith, E.L., and G.B. Ruyle. 1991. Considerations when monitoring rangeland vegetation. G.B. Ruyle. (ed). Some methods for monitoring rangelands and other natural area vegetation. University of Arizona, College of Agriculture, Extension Report 9043. p 3.